Each intervention group had comparable increases in physical
activity at 6 and 24 months, and the decline for each group from 6 to
24 months was similar. For cardiorespiratory fitness, both groups had
significant increases from baseline to 6 months, but members of the
structured exercise group increased their fitness significantly more
(P<.001). At 24 months, the increase in peak oxygen
consumption (VO2peak) was significantly higher
than at baseline and comparable in the 2 groups. From 6 to 24 months,
both groups had significant decreases in cardiorespiratory fitness, but
the decrease was significantly greater in the structured exercise group
than the lifestyle group (P<.001).

US Department of Health and Human Services, Centers for
Disease Control and Prevention, National Center for Chronic Disease
Prevention and Health Promotion. Physical Activity and Health: A
Report of the Surgeon General. Atlanta, Ga: Centers for Disease
Control and Prevention; 1996.

King AC, Haskell WL, Young DR, Oka RK, Stefanick ML. Long-term effects of varying intensities and formats of physical
activity on participation rates, fitness, and lipoproteins in men and
women aged 50 to 65 years. Circulation.1995;91:2596-2604.

Wood PD, Stefanick ML, Williams PT, Haskell WL. The
effects on plasma lipoproteins of a prudent weight-reducing diet with
or without exercise in overweight men and women. N Engl J Med.1991;325:461-466.

Context Even though the strong association between physical
inactivity and ill health is well documented, 60% of the population is
inadequately active or completely inactive. Traditional methods of
prescribing exercise have not proven effective for increasing and
maintaining a program of regular physical activity.

Conclusions In previously sedentary healthy adults, a
lifestyle physical activity intervention is as effective as a
structured exercise program in improving physical activity,
cardiorespiratory fitness, and blood pressure.

Sedentary habits account for a substantial portion of deaths due to coronary
heart disease,1,2 type 2 diabetes,3,4 and colon
cancer.5 In 1992, the American Heart Association named physical inactivity as an independent risk factor for cardiovascular
disease (CVD).6 Accumulating evidence also indicates that
an active and fit way of life helps preserve functional ability and
maintain independent living in older adults.7 Despite these documented benefits of exercise, fewer than one fifth of US adults
engage in regular, sustained, vigorous exercise; this fraction has not
increased since the mid-1980s.8

Understanding the causes of inactivity may help in developing effective
programs to increase the number of those who are inactive or
inadequately active to meet public health recommendations of 30 minutes
or more of moderate-intensity physical activity on most, preferably
all, days of the week.8,9 Barriers include lack of time,
lack of social support, inclement weather, disruptions in routine, lack
of access to facilities, and dislike of vigorous
exercise.10 Lifestyle programs that encourage accumulating
moderate-intensity physical activity through increasing behavioral
skills associated with adopting and maintaining activity have
been advocated as an alternative to vigorous fitness center–based exercise overcome these barriers.11,12

In this article, we compare the 24-month effects of a lifestyle
physical activity program designed to help participants overcome
activity barriers with a traditional structured exercise program. We
hypothesized that a behaviorally based lifestyle physical activity
intervention, in which individuals increase moderate-intensity physical
activity as part of their daily routines, would result in higher levels
of physical activity and cardiorespiratory fitness at 24 months
compared with baseline and that these levels of physical activity and
fitness would be higher in the lifestyle group when compared with a
traditional structured fitness center–based intervention. A secondary
aim of this study was to compare changes in CVD risk factors from
baseline to 24 months and between lifestyle and structured physical
activity interventions.

Methods

Study Participants and Design

The study protocol for this trial (known as Project
Active13) was conducted from August 1, 1993,
through July 31, 1997, and approved annually by the Cooper Institute
Institutional Review Board, Dallas, Tex. Each participant gave written
informed consent prior to testing and again prior to randomization. The
sample size was calculated to detect a 3-mL/kg per minute or 2-kcal/kg
per day difference between treatment groups at the end of 24 months,
and was based on a 24-month intervention of home-based structured
exercise in sedentary adults14 that produced a 10%
increase in peak oxygen consumption (VO2peak) or
approximately 3 mL/kg per minute. An energy expenditure of 2 kcal/kg
per day is 150 kcal/d for a 75-kg person or about 1000 kcal/wk (≈16
km of brisk walking for 1 week), and is the amount of exercise
recommended in Physical Activity and Health: A Report of the
Surgeon General.8 It is estimated that
this amount of
increased physical activity would be adequate to move sedentary,
low-fit individuals from the highest risk category into the moderately
active, moderately fit category.8 In addition to these
effect sizes, we also anticipated a 15% annual dropout rate, yielding
90% power at a .05 α level of significance. Based on these
parameters, the recruitment goal was determined to be 210 participants.

Study participants were 235 healthy sedentary men (n = 116) and women
(n = 119) aged 35 to 60 years who lived or worked within a 16-km
(10-mile) radius of our center. They were randomized to either a
lifestyle physical activity program or a structured exercise program
(Figure 1). Participants were
recruited in 3 cohorts, randomized at 6-month intervals. Exclusion
criteria were (1) self-reported history of myocardial infarction,
stroke, type 1 diabetes mellitus, osteoporosis, and osteoarthritis (if
it limited mobility); (2) weight more than 140% of ideal body weight;
(3) plans to move from the local area during the study period; (4) 3 or
more drinks of alcohol daily; (5) exercising at least 3 days a week for
20 minutes or more or having an estimated total energy expenditure
exceeding 36 kcal/kg per day (men) or 34 kcal/kg per day
(women)15; (6) blood pressure of
160/100 mm Hg or more; (7)
use of medication (such as β-blockers) that could impair exercise
performance; and (8) for women, plans to become pregnant in the next 2
years.

Clinical Measurements

Following telephone screening, eligible participants were invited to an
orientation session to obtain written informed consent and determine
baseline physical activity using the 7-Day Physical Activity Recall
(PAR).15 The
PAR estimates total energy expenditure by
asking participants to recall the amount of time spent in sleep and in
moderate, hard, and very hard activities during the previous 7 days and
multiplying time in each category by an established MET value
(1 MET is the metabolic equivalent at rest;
moderate-intensity activities are 3-6 times greater, or 3-6 METs).
Reliability and validity of the PAR have been established and have been
summarized by Pereira and colleagues.16 One experienced
interviewer conducted 95% of all PAR measurements. We also
determined the convergent validity of the PAR with concurrent
temporally matched data from the Tritrac R-3D (Hemokinetics Inc,
Madison, Wis) activity monitor in a subset of participants (n = 33) at
24 months. Correlations between estimated total energy expenditure
from the PAR and the
Tritrac R-3D regression equation ranged from
r = 0.86 to r = 0.95 across each of the 7 days.
Overall, these data support the use of the PAR as a primary outcome
measure for the present study (Gregory J. Welk, PhD; Raymond W.
Thompson, MA; Dan I. Galper, PhD; unpublished data, 1998). In addition,
we also asked about stairs climbed per day, minutes of walking per day,
and hours of sitting per week.

Participants completed medical history questionnaires at orientation.
Eligible participants were scheduled for laboratory assessments. A
physician reviewed the medical history and performed a physical
examination. We measured resting blood pressure in triplicate (seated)
by auscultatory techniques with a mercury
sphygmomanometer.17 Blood samples were drawn in the morning
after an overnight fast. All samples were analyzed for lipids and
lipoproteins in a Centers for Disease Control and Prevention
standardized laboratory.

Subjects who met eligibility criteria were scheduled for a second
laboratory examination. We measured weight, height, and estimated
percentage of body fat from 7 skinfold sites.18,19 All
individuals completed a maximal graded treadmill test,20
with VO2 measured with automated
cardiorespiratory monitoring techniques. Within 6 weeks of baseline
testing, men and women in each cohort were randomized into either
lifestyle or structured exercise groups. All measurements taken at
baseline screening were repeated after 6 and 24 months of intervention.
Following randomization, all measurement staff were blinded to the
participant's group assignment. Additional details on design and
methods are published elsewhere.13

Intervention

Psychological Model for Behavior Change. The Social Cognitive Theory21 with the Stages of
Motivational Readiness (Stages of Change) model22 is used to guide interventions for a number of health behaviors (eg, smoking
cessation and diet)23 and in a variety of settings (eg,
communities and physicians' offices).24,25 The Stages of
Change model proposes that individuals differ in their motivational
readiness for change. They may be (1) not intending to change, (2)
intending to change, (3) making small changes, (4) meeting a behavior
change criterion (eg, meeting public health recommendations of
accumulating ≥30 minutes of moderate-intensity activity on most days
of the week9), or (5) sustaining the change over time.
Fundamental to the model are 10 cognitive and behavioral strategies to
help people progress from lower to higher levels of motivational
readiness. These 10 skills include 5 cognitive strategies aimed at
changing ways of thinking and 5 behavioral strategies aimed at
increasing specific behaviors. This model was used in both groups, and
its implementation is described more completely
elsewhere.13,26

Intervention Procedures. Participants in both groups received 6 months of intensive
intervention and 18 months of maintenance intervention. The physical
activity goal for both groups at 6 months was to increase energy
expenditure by 3 kcal/kg per day and increase fitness
(VO2peak) by 5 mL/kg per minute, then to
maintain an increase in physical activity of 2 kcal/kg per day and 3
mL/kg per minute at the end of 24 months.

Participants randomized to the structured exercise group received a
traditional exercise prescription (exercise intensity of 50%-85% of
maximal aerobic power for 20-60 minutes).27 Individual
supervised sessions were offered 5 days per week for 6 months at a
state-of-the-art fitness center. We asked participants to initially
attend at least 3 supervised sessions per week and to gradually
increase to 5 days per week. Initial levels and progression of exercise
dosage followed American College of Sports Medicine
recommendations.27 Group leaders helped participants learn
to set realistic physical activity goals, monitored their physical
activity, and provided verbal reinforcement. Following 3 weeks of
initial instruction and supervised exercise, structured exercise group
participants chose the aerobic activities they most enjoyed and
individualized their programs among all activities available at the
center. Participants who failed to attend at least 1 session per week
were contacted and encouraged to return to a regular schedule of
exercise. During the 18-month follow-up intervention, the group met
quarterly for group activities. They also received a monthly activities
calendar and a quarterly newsletter on the benefits of activity and
research findings related to physical activity.

Participants randomized to the lifestyle group were advised to
accumulate at least 30 minutes of moderate-intensity physical
activity on most, preferably all, days of the week, in a way uniquely
adapted to each person's lifestyle. They were encouraged to progress
toward this goal in a manner best suited for their level of
motivational readiness for change. In the format of small groups that
met for an hour 1 night a week for the first 16 weeks, then biweekly
until week 24, participants learned cognitive and behavioral strategies
found to be related to physical activity behavior. Meetings were held
in a small classroom setting and participants in this group were not
provided free membership to the fitness center facilities. Group
facilitators worked weekly with participants using a problem-solving
approach to discuss cognitive and behavioral strategies and techniques
to help them initiate, adopt, and maintain a physical activity program.
Participants were assessed on Stages of Change each month and were
given an intervention manual tailored for their level of
readiness.23 We gave
weekly home assignments aimed at
enhancing behavioral skills and problem solving. During the 18-month
follow-up, meetings decreased at 6-month intervals to monthly, then
bimonthly, and finally trimonthly. Group meetings consisted of a
variety of activities that included a mall walk, orienteering,
volleyball, and a life-size board game designed to reinforce cognitive
and behavioral skills. Participants also received a monthly activities
calendar and a quarterly newsletter.

Data Analysis

Statistical comparisons between intervention groups were made using all
available data (Figure 1), with participants
grouped as originally randomized, regardless of
the degree of intervention compliance or types of activities actually
performed. We did not impute values for any missing data for
participants who did not complete some clinical and laboratory
measurements. At 6 and 24 months, we used analysis of
covariance28 to assess changes
after baseline in physical
activity, cardiorespiratory fitness, blood pressure, lipoprotein
levels, and body composition. The change in each clinical outcome
measure was compared between interventions with adjustment for the
baseline measure and for age, sex, body mass index (BMI, calculated as
weight in kilograms divided by the square of height in meters), cohort,
and ethnicity. The latter covariates were selected a priori. Summary
changes are reported as adjusted least squares means,29
standardizing changes for possible covariate imbalances between
treatments. Six-month changes in physical activity, cardiorespiratory
fitness, CVD risk factors, and psychosocial measures are
presented elsewhere.26,30 In this article, we present
changes from baseline to 24 months and from 6 to 24 months to determine
whether changes were maintained over the longer-term follow-up. All
data analyses were performed using SAS software, Version
6.28
All reported P values are 2-tailed.

Results

Baseline Characteristics and Measurement Adherence

Selected baseline characteristics for the 235 participants included in
the efficacy population are shown in Table 1. The mean (SD) age of study
participants was 46.0 (6.6) years. All were sedentary and most were
moderately overweight. The group had normal blood pressure levels and
lipoprotein profiles and few were cigarette smokers.

We randomized 122 participants into the lifestyle exercise program and
115 into the structured exercise program in 3 separate recruitment
cohorts at 6-month intervals. Each cohort was randomized in a 1-week
period prior to the start of the intervention. During the first month
of the intervention period, 1 man in the lifestyle group and 1 woman in
the structured exercise group were dropped from the study because of
clinical manifestation of heart disease that made their participation
unsafe. These adverse events did not occur during exercise. At 6
months, 109 lifestyle group and 103 structured exercise group
participants completed the examination in full or in part, and 100 and
90 participants, respectively, completed the 24-month examination in
full or in part. Differences between interventions in completion rates
were not significant (Figure 1).

Summary of 6-Month Results

Results after 6 months of intervention are reported in full
elsewhere.26,30 Briefly, both groups significantly
increased physical activity and cardiorespiratory fitness. The
structured exercise group increased their cardiorespiratory fitness
significantly more than the lifestyle group, but at 6 months, the
groups had comparable increases in physical activity. Both groups had
similar significant improvements from baseline to 6 months for ratio of
total cholesterol level to high-density lipoprotein cholesterol (HDL-C)
level, systolic and diastolic blood pressure, and percentage of body
fat.

Major Findings at 24 Months

Primary Outcomes—Physical Activity and Cardiorespiratory Fitness.Table 2 shows changes from baseline
to 24 months as least squares adjusted means, adjusted for
between-intervention differences in the covariates. Both lifestyle and
structured exercise groups significantly increased total energy
expenditure from baseline to 24 months (P<.001 and
P = .002, respectively). Components of the physical activity
measure show that lifestyle-group participants increased their
moderate-intensity physical activities nearly 3 times more than
structured exercise group participants (P<.001 and
P = .18, respectively). The structured exercise group had a
more than 2-fold increase in their vigorous activities (hard and very
hard) compared with the lifestyle group (P = .008 and
P<.001, respectively). However, these measures were not
significantly different between the 2 groups (P = .63 for
moderate and P = .08 for vigorous).

Both groups increased their cardiorespiratory fitness from baseline to
24 months (P = .002 for lifestyle and P<.001 for
structured exercise), with no significant difference between groups
(P=.22). The distribution of cardiorespiratory
fitness changes (not shown) indicates that 21% of lifestyle group and
30% of structured exercise group participants increased their
cardiorespiratory fitness by 10% or more from baseline.

In addition, we compared these results with the
last-observation-carried-forward (LOCF) method by replacing missing
values with 6-month or baseline measures if we did not have 24-month
measures. We did not find that the LOCF method changed the nominal
significance of the results in any way. For example, by not imputing
values for VO2peak and energy expenditure, the
mean adjusted changes, respectively, were 0.77 mL/kg per minute and
0.84 kcal/kg per day for the lifestyle group, and 1.34 mL/kg per minute
and 0.69 kcal/kg per day for the structured exercise group. Using the
LOCF method, the results for VO2peak and energy
expenditure, respectively, were 0.77 mL/kg per minute and 0.83 kcal/kg
per day for the lifestyle group and 1.72 mL/kg per minute and 0.77
kcal/kg per day for the structured exercise group. For the lifestyle
group, the results were nearly identical while for the structured
exercise group, these results were somewhat higher because their
results were higher at 6 months. A second LOCF analysis in which only
baseline data were used to impute missing 24-month results also showed
little change from the original analysis.

Maintenance of Physical Activity and Cardiorespiratory Fitness From
6 to 24 Months. We evaluated maintenance of physical activity and
cardiorespiratory fitness from baseline to 6 months and 24 months
(Figure 2). Both groups had similar
increases in physical activity at 6 months and similar decreases from
6 to 24 months (0.7 kcal/kg per day
[P = .005] and 0.8 kcal/kg per day
[P = .02] for lifestyle and structured exercise groups,
respectively). These decreases were not significantly
different (P = .83).

Maintenance of physical activity also could be defined as the
percentage of individuals meeting or exceeding public health
recommendations for physical activity, defined in Physical
Activity and Health: A Report of the Surgeon General as increasing
physical activity by 150 kcal/d.8 Examination of the
distribution of physical activity changes (not shown) indicates that
in each group, 20% met or exceeded the public health
recommendations.8

Figure 2 (bottom) shows increases in both groups for cardiorespiratory
fitness from baseline to 6 months. Fitness
(VO2peak) increased 1.58 mL/kg per minute
(P<.001) in the lifestyle group and 3.64 mL/kg per minute
(P<.001) in the structured exercise group. There was a
significant between-group difference at 6 months (P<.001).
From 6 to 24
months, the lifestyle group decreased
VO2peak by 0.7 mL/kg per minute (P =.04)
and the structured exercise group decreased their
VO2peak by 2.4 mL/kg per minute (P<.001).
The decreases in fitness from 6 to 24 months were
significantly different (P<.001) and by 24 months, both
groups were comparable.

A second way that we examined the issue of maintenance of
activity during the follow-up period was to ask individuals what
percentage of the 72 weeks in the 18-month maintenance period they were
regularly active at a moderate intensity. We defined regular physical
activity as performing 30 minutes of moderate-intensity physical
activity each day for at least 5 days of the week. Participants checked
the percentage from 0% to 100% (in 10-unit increments). Thirty-nine
percent of lifestyle and 35% of structured exercise participants said
they had maintained their activity during 70% or more of the weeks for
the last 18 months. Twenty-nine percent of lifestyle and 24% of
structured exercise participants said they maintained activity 40% to
60% of the time, and 32% of lifestyle and 40% of structured exercise
participants said they maintained their activity 0% to 30% of the
time. Because there was no significant difference between the 2 groups
in maintenance of activity, data were combined to examine the
dose-response relationship between maintenance and primary and
secondary outcomes. Regression analyses indicated that for all
outcomes, those who responded that they were active 70% or more of the
time had at least twice as much improvement compared with those
who did not (P<.01). For example, the increase in total
activity was 1.29 kcal/kg per day for those who maintained 70% or more
compared with 0.28 kcal/kg per day for those in the lowest 30%.
Similarly, for physiological outcomes, weight was decreased by 0.88 kg
for those who maintained 70% or more compared with an increase of 2.48
kg for those who maintained 30% or less. Systolic and diastolic blood
pressure and total cholesterol level showed greater improvements for
those who maintained 70% or more (−5.31 mm Hg, −9.12 mm Hg, and
−0.43 mmol/L [−16.7 mg/dL], respectively, compared with −2.6 mm
Hg, −5.18 mm Hg, and −0.22 mmol/L [−8.37 mg/dL] for those who
maintained ≥30%).

Sex Differences in Primary Outcomes. Although this study was not powered to examine the effect of sex on
outcomes, we did observe some within-sex differences between lifestyle
and structured exercise participants in 24-month changes in physical
activity and fitness. However, these differences were variable and none
were statistically significant. But there were significant
within-treatment differences between men and women in 24-month changes
in fitness, with greater increases in men than women in each treatment
group (P<.001). The corresponding sex differences in changes
in total and vigorous activity were consistent in direction across
treatments, with greater increases in men than women, but these
differences were not significant (P = .59 for total activity
and P = .11 for vigorous activity).

Secondary Outcomes—CVD Risk Factors.Table 2 shows adjusted mean changes in CVD risk factors. Changes in
systolic and diastolic blood pressure were significantly different from
baseline to 24 months for both intervention groups. In examining the
changes in systolic and diastolic blood pressure from 6 to 24 months,
diastolic blood pressure but not systolic blood pressure continued to
improve. The mean (SE) decrease in diastolic blood pressure from 6 to
24 months was −3.16 (0.82) mm Hg (P<.001) for the lifestyle
group and −2.66 (0.86) mm Hg (P = .002) for the
structured exercise group.

None of the lipid or lipoprotein measures changed from
baseline to 24 months in the lifestyle group, but total cholesterol,
low-density lipoprotein cholesterol (LDL-C), and HDL-C measures
decreased significantly for the structured exercise group, and the
ratio of total cholesterol to HDL-C increased significantly in this
group. From 6 to 24 months, none of the lipid measures significantly
changed for either intervention group, except that the ratio of total
cholesterol to HDL-C increased significantly in both groups
(P = .03 for lifestyle and P<.001 for structured
exercise).

Body weight was unchanged from baseline to 24 months, but
percentage of body fat decreased significantly in both intervention
groups (P<.001) (Table 2). Participants in the lifestyle
group had no significant change in weight (mean [SE], 0.41 [0.46]
kg; P = .37) from 6 to 24 months, but percentage of body fat
decreased (−1.13% [0.29%]; P = .001) significantly. The
structured exercise group increased their weight (2.10 [0.49] kg;
P<.001) from 6 to 24 months with no change in percentage of
body fat (−0.07% [0.31%]; P = .82). These 6- to
24-month changes in weight and percentage of body fat differed
significantly (P = .01) between the 2 intervention groups.

Comment

The principal finding from this study is that both the lifestyle
and the structured interventions produced significant and comparable
beneficial changes in physical activity, cardiorespiratory fitness,
blood pressure, and percentage of body fat at 24
months compared with baseline measures. This
supports the hypothesis that a behaviorally based lifestyle physical
activity intervention can significantly increase physical activity and
fitness by 24 months. The novel finding is that this approach is as
effective in producing beneficial changes in physical activity,
cardiorespiratory fitness, blood pressure, and body composition as the
traditional structured approach. For sedentary persons whose barriers
to physical activity may include lack of time, dislike of vigorous
exercise, or lack of access to facilities, this is good news. It means
that health care professionals who are counseling their patients about
physical activity can provide options beyond traditional fitness
center–based recommendations.

There were no significant differences between lifestyle and
structured exercise groups in changes for any of the primary or
secondary outcome measures from baseline to 24 months. This finding is
contrary to our hypotheses that the lifestyle group would do
significantly better at 24 months while the structured exercise group
would return to baseline levels 24 months later. At 6 months, the
structured exercise group had increased their fitness nearly 2 times
more than the lifestyle group, but by 24 months the 2 groups were
nearly equivalent on every measure. In the 18-month follow-up
period, there was a greater decline in fitness and a greater increase
in weight in the structured exercise group, whereas the lifestyle group
significantly decreased percentage of body fat from 6 to 24 months.
Although both groups declined in physical activity and
cardiorespiratory fitness, there was a greater decline in the
structured exercise group, which suggests this group was not able
to maintain its physical activity routines as effectively as the
lifestyle group. Nevertheless, the structured exercise group did better
than expected, perhaps because of delivering an enhanced structured
intervention that included goal setting, self-monitoring, and
reinforcement for reaching goals in addition to skills related to
increasing physical fitness. Additional analyses from this study
indicate that the lifestyle group was significantly more
cost-effective, with total costs of about one third to one fourth of
the structured exercise group (Mary A. Sevick, ScD; A.L.D.; Melba S.
Morrow, MA; B.H.M.; John Chen, MD, PhD; S.N.B.; unpublished data,
1998).

Our lifestyle physical activity approach differs from other
lifestyle interventions previously published31- 33 because
we focused on a single risk factor (ie, physical inactivity) vs
multiple risk factors (eg, high-fat diet, high sodium, and physical
inactivity). Although we did not intervene on diet behavior, we did
measure diet with 3-day diet records in our sample. Preliminary
analyses indicate that participants did not significantly change their
dietary behavior as a result of either lifestyle or structured exercise
interventions. At baseline, 6 months, and 24 months, both groups had
comparable values on all dietary variables. We believe the changes or
lack of changes in some CVD risk factors are consistent with this
finding. For example, the changes in blood pressure are consistent with
recommending moderate-intensity exercise for lower blood
pressure.34 Furthermore, to
achieve changes in lipids or
weight, most studies indicate that changing dietary behavior as well as
performing vigorous exercise yields the most
improvement35,36; thus, it is not surprising that our
participants did not significantly experience changes in lipid levels
or decrease weight. It is of practical importance that our participants
lost body fat and that the lifestyle group did not gain weight during
the 24-month period because some studies show weight gain in sedentary
controls over even shorter periods.37

Changes in physical activity, cardiorespiratory fitness, and CVD
risk factors were well maintained during the follow-up period from 6 to
24 months, unlike the results recently reported by Wing et
al.33 Our results are
comparable to those reported by King
et al,14 in which individuals assigned to a home-based
exercise program significantly increased activity and fitness levels
and remained significantly higher at 24 months compared with baseline.

Even though the mean increases over 24 months in physical
activity and cardiorespiratory fitness were statistically significant,
some may not consider them to be practically significant. We believe it
is important to examine these changes within a public health context.
The increases may seem small, but in examining the distributions of
change in physical activity, one fifth of initially sedentary
participants were achieving or exceeding public health recommendations
for physical activity at the end of 24 months. Furthermore, at
the end of 24 months, at least one fourth of participants had
maintained an increase in cardiorespiratory fitness of 10% or more. A
previous study of change in fitness among men demonstrates that a 2-MET
increase in maximal treadmill performance was associated with a 30%
reduction in mortality.38 Accordingly, we
estimate that the
10% increase in treadmill performance in this study might result in a
15% reduction in mortality. If this intervention were widely
disseminated in an efficacious manner, it could have far-reaching
positive effects on the public's health. Further studies are needed to
examine whether lifestyle approaches can be efficacious in other
settings, populations.

This study has several potential limitations. The study protocol did
not include a "no treatment" control group. This control condition
was not incorporated into the original design because physical
inactivity increases the risk for several chronic diseases and
decreases longevity.7,9- 11 We considered it unethical to
incorporate a treatment condition that did not encourage and promote
physical activity over a 2-year period. Instead, we chose a study
design similar to other clinical trials, in which a novel treatment
(ie, lifestyle) is compared with a usual treatment (ie, structured). As
to the generalizability of these results, our study participants were
highly educated. However, we did not find differences across
educational levels on any of the primary or secondary outcome
variables.

This is, to our knowledge, the first demonstration that a lifestyle
approach to increasing physical activity in previously sedentary
healthy adults is as effective over 24 months as more traditional
structured exercise approaches. Our results show that sedentary but
otherwise healthy individuals can make significant improvements in
physical activity, cardiorespiratory fitness, and CVD
risk factors without having to go to a
fitness center and perform high-intensity workouts. It is likely that
many clinicians could promote the recent public health recommendations
of 30 minutes of moderate-intensity physical activity on most days of
the week8,9 and be assured that patients who adhere will
achieve positive health benefits. Counseling patients to fit
moderate-intensity activity into daily life may have significant health
benefits and could aid public health efforts to reduce the prevalence
of sedentary lifestyles.

US Department of Health and Human Services, Centers for
Disease Control and Prevention, National Center for Chronic Disease
Prevention and Health Promotion. Physical Activity and Health: A
Report of the Surgeon General. Atlanta, Ga: Centers for Disease
Control and Prevention; 1996.

King AC, Haskell WL, Young DR, Oka RK, Stefanick ML. Long-term effects of varying intensities and formats of physical
activity on participation rates, fitness, and lipoproteins in men and
women aged 50 to 65 years. Circulation.1995;91:2596-2604.

Wood PD, Stefanick ML, Williams PT, Haskell WL. The
effects on plasma lipoproteins of a prudent weight-reducing diet with
or without exercise in overweight men and women. N Engl J Med.1991;325:461-466.